Barrels of an anti-aircraft gun and an APC are seen outside the administration building in Donetsk, Ukraine, on May 29, 2014. / Ivan Sekretarev, AP

by Jim Michaels, USA TODAY

by Jim Michaels, USA TODAY

WASHINGTON - After months of hesitation, Ukraine is pressing a military offensive against pro-Russian militias operating in the east, intensifying the bloodshed in a risky gambit to quickly crush the revolt.

On Thursday, rebels struck back, downing a military helicopter and killing at least 12 people aboard, including a general, outside the city of Slovyansk.

The shoot-down followed a battle over the airport at Donetsk in which dozens of militants were killed this week.

The military offensive comes as Ukraine's government has been bolstered by a mostly successful election on Sunday and remarks by Russian President Vladimir Putin suggesting he would respect the results of the vote.

Russia also appears to be reducing its support to militias operating in eastern Ukraine, providing an opening for its military to move against the rebellion.

"That signaled to the military (it was time) to re-establish security," said Kevin Ryan, a retired brigadier general at Harvard's Belfer Center.

Shortly after winning the presidential election Sunday, Petro Poroshenko pledged to stamp out the rebellion in the east.

Ukraine's recent military response stands in contrast to its more passive reaction when Russian forces invaded Crimea in February when troops remained on their bases before withdrawing from the region.

Ukraine's military response to subsequent pro-Russian militia activity in eastern Ukraine had also been hesitant until recently, though the army has had numerous clashes with pro-Russian militants.

Much of the hesitation stemmed from the confusion that followed the popular revolt that pushed Viktor Yanukovych from office, touching off the current crisis.

"The state had collapsed when (Yanukovych) collapsed," said Stephen Blank, a senior fellow at the American foreign Policy Council.

The scale of the recent fighting at the Donetsk airport marks a departure in tactics.

The new offensive, however, risks escalating the conflict even further, particularly if pro-Russia militias are determined to keep fighting and the unrest spreads to other cities. Urban warfare favors insurgents who can seek cover among civilians and neutralize the firepower advantage of conventional forces.

So far, Ukraine's military has limited itself to attacking rebels in open areas where they can minimize civilian casualties, Ryan said.

Ukraine's army is not well trained and has been starved for resources, particularly in the past decade, said Olga Oliker, an analyst at RAND Corp.

The Pentagon has said it has supplied Ukraine's military with non-lethal aid, such as food rations, but has not provided arms and ammunition.

Ukraine's conventional army is not suited for the type of counterinsurgency operations that would be required if the country is sucked into a broader conflict, analysts said.